1. Field of the Invention
The present invention pertains generally to a medical device useful for delivering a substance to a biological passageway. More specifically, the present invention pertains to a catheter device having a syringe assembly useful for delivering a therapeutic substance to a passageway, such as a blood vessel.
2. Description of the Related Art
Percutaneous transluminal coronary angioplasty (PTCA) is a procedure for treating heart disease. A catheter assembly having a balloon portion is introduced percutaneously into the cardiovascular system of a patient via the brachial or femoral artery. The catheter assembly is advanced through the coronary vasculature until the balloon portion is positioned across the occlusive lesion. Once in position across the lesion, the balloon is inflated to a predetermined size to radially compress the atherosclerotic plaque of the lesion against the inner wall of the artery to dilate the lumen. The balloon is then deflated to a smaller profile to allow the catheter to be withdrawn from the patient's vasculature.
Restenosis of the artery commonly develops over several months after the procedure, which may require another angioplasty procedure or a surgical by-pass operation. Restenosis is thought to involve the body's natural healing process. Angioplasty or other vascular procedures injure the vessel walls, removing the vascular endothelium, disturbing the tunica intima, and causing the death of medial smooth muscle cells. Excessive neoinitimal tissue formation, characterized by smooth muscle cell migration and proliferation to the intima, follows the injury. Proliferation and migration of smooth muscle cells (SMC) from the media layer to the intima cause an excessive production of extra cellular matrices (ECM), which is believed to be one of the leading contributors to the development of restenosis. The extensive thickening of the tissues narrows the lumen of the blood vessel, constricting or blocking blood flow through the vessel.
To reduce the chance of the development of restenosis, therapeutic substances are administered to the treatment site. For example, anticoagulant and antiplatelet agents are commonly used to inhibit the development of restenosis. In order to provide an efficacious concentration to the target site, systemic administration of such medication often produces adverse or toxic side effects for the patient. Local delivery is a preferred method of treatment in that smaller total levels of medication are administered in comparison to systemic dosages, but are concentrated at a specific site. Local delivery, thus, produces fewer side effects and achieves more effective results.
One commonly applied technique for the local delivery of a therapeutic substance is through the use of a medicated, implantable prosthesis, one example of which includes a stent. A stent coated with a polymeric carrier, which is impregnated with a therapeutic substance, can be deployed at a selected site of treatment. The polymeric carrier allows for a sustained delivery of the therapeutic substance. A disadvantage associated with the use of medicated stents is that the quantity of the substance that can be impregnated in the polymeric carrier is limited. In order to increase the capacity of the polymeric carrier, the amount of polymeric material employed, and in effect the thickness of the coating, must be increased to accommodate the quantity of the substance used. An increase in the profile of the coating significantly limits the applications for which the stents can be used.
Another disadvantage associated with the use of medicated stents is that the polymeric carrier is only capable of applying the therapeutic substance to the inner surface of the tunica intima layer of the vessel. The polymeric carrier is incapable of significantly introducing a therapeutic substance to the tunica adventitia or the tunica media layers of the vessel. Accordingly, it is desirable to provide a substance delivery apparatus which is capable of applying any desired amount of therapeutic substances to the tunica adventitia and media layers to inhibit migration of SMC and the development of ECM.
Another commonly applied technique for the local delivery of a therapeutic substance is through the use of porous balloons attached to a distal end of a catheter assembly. The expansion of the balloon, which in effect results in the dilation of the occluded region, is accomplished by injecting a therapeutic substance into the balloon. The use of a therapeutic substance as an expansion fluid additionally functions as a medicament for the diseased region, as the therapeutic substance is discharged from the porous balloon during and subsequent to the expansion therapy. A shortcoming associated with this procedure is that the therapeutic substance is contiguously carried off in the patient's blood stream as it is being discharged from the balloon, which results in an ineffective treatment of the target site and adverse exposure of the substance to healthy tissues. Accordingly, it is desirable to provide a substance delivery apparatus that is capable of applying a therapeutic substance to the diseased region without significant loss of the substance caused by the downstream flow of blood.